Method and apparatus for operation of a positively driven steam generator with rolled overlap and gastight welded vaporizer walls

ABSTRACT

A method of and arrangement for operating a steam generator with forced circulation and with circulation overlap and gastight welded evaporator walls, in which saturated steam freed in a separator vessel is conveyed not only to succeeding superheaters, but also through a withdrawal conduit and a control valve to a heat exchanger preceding the steam generator or its evaporator, and in which the said saturated steam is employed for heating up the feed water to a temperature which is as close as possible to the pertaining saturation temperature.

0 United States Patent 1 1 3,580,223

[72] Inventor Klaus Knizia [56] References Cited 2 A l N gg a Enslskirchen, Germany UNITED STATES PATENTS 1] P 2 921,441 H1960 Buri 122/1x [22] Filed Apr. 24, 1969 3,008,295 11/1961 Profos 122/406X [45] Patented May 25, 1971 3,361,117 2/1968 Batyko..... 122/406X [73] Assgnee 3 478 726 11/1969 Kikinis 122/406 G as y Primary Examiner-Kenneth W. Sprague Attorney-Walter Becker [54] OF ABSTRACT: A method of and arrangement for operating a steam generator with forced circulation and with circulation WITH ROLLED OVERLAP AND GASTIGHT overlap and gastlght welded evaporator walls, in which satu- WELDED VAPORIZER WALLS d l d l 2 Cl 1 Drawing Fig. rated steam free in a separator vesse 1s conveve not on y to succeeding superheaters, but also through a withdrawal con- [52] US. Cl 122/1, duit and a control valve to a heat exchanger preceding the 60/89, 122/406 steam generator or its evaporator, and in which the said satu- [51] Int. Cl F22b 29/06 rated steam is employed for heating up the feed water to a [50] Field of Search 122/ 1,406, temperature which is as close as possible to the pertaining 406 (S), 406 (SU), 89; 60/105, 106, 107

saturation temperature.

Patented May 25, 1971 METHOD AND APPARATUS FOR OPERATION OF A POSITIV ELY DRIVEN STEAM GENERATOR WITH ROLLED OVERLAP AND GASTIGI-IT WELDED VAPORIZER WALLS The present invention relates to a method of and apparatus for operating a steam generator with forced circulation and with circulation overlap and with gastight welded evaporator walls.

Of the heretofore known steam-generating methods accord ing to the natural circulation, according to the La Mont principle, and according to forced circulation, the forced circulation is employed primarily with large units inasmuch as it makes possible high antropy of the water vapor which high antropy is required for an economic process.

Inasmuch as with pure forced circulation at low loads and during the starting and stopping phases under certain conditions the evaporator of the steam generator has not available a sufficiently large mass flow, and since, therefore, a sufficient cooling of the lower walls is not assured, modifications of the pure forced circulation by an additional circulation overlap has been developed during the last years. To this end, there is primarily employed a separating vessel with a circulating pump, which vessel follows the evaporator and permits at the above-mentioned load conditions the separation of the water possible at this place into a liquid phase and a vapor phase. The water will then by means of the circulating pump again be conveyed to the evaporator and in this way the mass flow passing through said evaporator and the inlet anthalpy of the water will be increased.

This method, however, is not sufiicient for steam generators with gastight welded evaporator walls. The reason for this is that the feed water enters the evaporator at a temperature which is considerably less than the saturation temperature so that by the returned water the mass flow is sufficiently increased but not the inlet temperature after the mixture. It is desirable that the temperature of the medium at its entry into the evaporator has approximately the magnitude of the saturation temperature because in such an instance in the evaporator the entire increase in anthalpy in the feed water can be carried out at constant temperature so that the medium will not cause any additional temperature stresses in the walls. The circulation overlap will furthermore not be carried out over the entire load range but will be turned off at a certain load in which instance the feed water inlet anthalpy and thus also the temperature in the evaporator will be considerably less than the pertaining saturation temperature.

In contrast to the above-mentioned method, there is recently employed an operational method which is termed combined circulation." This method requires that the steam generator is operated overcritically over the entire load range while from a superheater surface of said steam generator a heated-up partial flow is returned to its inlet area where the required heating up of the medium is effected. This method hasthe drawback that it can be employed only in the overcritical range which excludes from the start an advantageous operation of the power plant block under slide pressure (Gleitdruck) and furthermore requires an additional pump in the main feed water flow which pump when failing in operation impairs the economy of the entire power plant block.

it is, therefore, an object of the present invention to provide a method of operation of a steam generator operated with forced circulation and circulation overlap and with gastight welded evaporator walls which will overcome the above-mentioned drawbacks.

It is another object of this invention to provide a method of operating a steam generator of the above-mentioned type which for dynamic operations of an increase in the load will permit maintaining the temperature of the working medium at its inlet in the evaporator at approximately the magnitude of the saturation temperature.

These and other objects and advantages of the invention will appear more clearly from the following specification, in connection with the accompanying drawing showing a diagram illustrating the method according to the invention.

The method according to the invention is characterized primarily in that the saturated steam freed in the separator vessel is conveyed not only to the succeeding superheaters, but is also through a withdrawing conduit and a control valve conveyed to a heat exchanger preceding the steam generator or its evaporator and is employed for heating up the feed water to a temperature which will be as close as possible to the pertaining saturation temperature.

The method according to the present invention while not limited to is preferably carried out by a heat exchanger comprising a plurality of high-pressure preheaters of the regenerative preheating type, which heat exchanger is designed for a higher designed pressure (Konzessionsdruck) than for the maximum tap pressure. In this way it is possible by means of the steam of higher pressure which steam is withdrawn from the separator vessel and which pressure may be reduced by a valve, favorably to influence the inlet temperature of the feed water.

Referring now to the drawing in detail, similar to the forced circulation method with circulation overlap, also with the method according to the invention, one or more separator vessels 5 are arranged behind the evaporator 3 and the economizer 2. It is in these separator vessels that the liquid phase is separated from the vapor phase. Additionally, the heat exchanger 1 is interposed either in the feed water flow 18 ahead of the boiler or for instance also behind the economizer 2 which means in the boiler. This heat exchanger is supplied with steam through conduits l3 and control valve 12 which steam was separated from the liquid phase in the separator vessel 5. The liquid water obtained in the separator 5 is through the governor 10, the conduit 19, and the circulating pump 6 pressed back into the boiler as is the case with the above-described circulation overlap.

If now the steam generator is started, first up to the first steam development in the pressureless system the feed water obtained in the separator vessel 5 is conveyed to the circuit in the manner described above. With increasing pressure and increasing development of steam, the water obtained in the separator vessel 5 will increase as to its saturation temperature and with regard to its saturation anthalpy. The admixture of this water to the incoming feed water alone would not be suffrcient to heat the feed water even approximately to the saturation temperature pertaining to the pressure at which the generator is operated. Consequently, through conduit 13 and the control valve 12, the heat exchanger 1 receives steam obtained in the separator vessel 5 and in this way an additional heating up of the feed water to the saturation temperature or a temperature considered admissible below the saturation temperature is effected. From the heat balance it will be obtained that with this heating up operation the quantity of steam available for cooling the superheater 4 is not reduced with regard to the pressure circulation operation. With increasing output of the block, the liquid obtained in the separator vessel 5 is reduced, and finally the circulation operation through the separator vessel 5 alone is stopped completely. The operation of the heat exchanger 1 with saturated steam from the conduit 13 may, however, through the control valve 12 be continued as long as desired for protecting the evaporator against inadmissible temperature differences at the side of the medium, i.e. within the pipes. It is also possible, instead of the heat exchanger 1 to employ one or more high-pressure preheaters of the regenerative preheating system and to supply said highpressure preheater or preheaters with steam from the conduit 13 through the control valve 12. By means of the deheater 17 it will be assured that the heat exchanger 1 not be supplied once with overheated steam withdrawn from the turbine 14 through conduit 15 and then again with saturated steam from the boiler. A control means 16 will see to it that the steam of higher pressure which steam is withdrawn from the separator vessel 5 through conduit 13 will not be supplied to the deheater 17 but will be conveyed to the heat exchanger 1. At the inlet 20 of the conduit 13 into the conduit 21 there is provided a further control means 22. lnasmuch as it is possible by means of the control valve 12 to obtain in the heat exchanger l a higher pressure than would correspond to the pertaining withdrawal steam flow, it is possible for dynamic operations of the increase in the load to adjust the feed water inlet anthalpy and thus the inlet temperature at the evaporator inlet as it is desired for operating the system so that it is subject to the least stresses.

The steam which is withdrawn from the turbine 23 through the conduit 24 is condensed in the condenser 25 and the condensate is by the condensate pump 26 and through conduit 27 with the interposition of a heat exchanger 28 adapted to be acted upon by tap steam conveyed through conduits 29 to the feed water container 8. From this container 8 the heat exchanger 1 is provided with feed water by means of the feed water pump 7 through the feed water conduit 30. Furthermore, through conduit 31 communicating with the feed water container 8, tap steam may be conveyed to the feed water for heating up the same.

It is, of course, to be understood that the present invention is by no means limited to the particular method and operation set forth above, but also comprises modifications within the scope of the appended claims.

I claim:

1. A steam generator with forced circulation and circulation overlap, which includes a circuit comprising: feed water pump means, separator vessel means for separating saturated steam from water, first conduit means leading from said feed water pump means to said separator vessel means, heat exchanger means interposed in said first conduit means between said feed water pump means and said separator vessel means, second conduit means leading from said separator vessel means to said heat exchangermeans for conveying to the latter saturated steam separated in said separator vessel means, control valve means interposed in said second conduit means, super heater means, third conduit means communicating with said separator vessel means and said super heater means for conveying to the latter saturated steamseparated in said separator vessel means, fourth conduit means adapted to establish communication between said super heater means and said heat exchanger means, and turbine means interposed in said fourth conduit means between said super heater means and said heat exchanger means, said fourth conduit means also having deheater means interposed between said turbine means and said heat exchanger means.

2. A steam generator according to claim 1, which includes additional turbine means operatively connected to said firstmentioned turbine means and having a steam outlet, fifth conduit means leading from said steam outlet to said feed water pump means, and condenser means as well as additional heat exchanger means and feed water container means serially arranged in said fifth conduit means between said additional turbine means and said feed water pump means. 

1. A steam generator with forced circulation and circulation overlap, which includes a circuit comprising: feed water pump means, separator vessel means for separating saturated steam from water, first conduit means leading from said feed water pump means to said separator vessel means, heat exchanger means interposed in said first conduit means between said feed water pump means and said separator vessel means, second conduit means leading from said separator vessel means to said heat exchanger means for conveying to the latter saturated steam separated in said separator vessel means, control valve means interposed in said second conduit means, super heater means, third conduit means communicating with said separator vessel means and said super heater means for conveying to the latter saturated steam separated in said separator vessel means, fourth conduit means adapted to establish communication between said super heater means and said heat exchanger means, and turbine means interposed in said fourth conduit means between said super heater means and said heat exchanger means, said fourth conduit means also having deheater means interposed between said turbine means and said heat exchanger meaNs.
 2. A steam generator according to claim 1, which includes additional turbine means operatively connected to said first-mentioned turbine means and having a steam outlet, fifth conduit means leading from said steam outlet to said feed water pump means, and condenser means as well as additional heat exchanger means and feed water container means serially arranged in said fifth conduit means between said additional turbine means and said feed water pump means. 